Housingless plate heat exchangers are known, for example, from German Laid-Open Application 41 25 222 A1 and U.S. Pat. No. 4,708,199, and are proposed therein as water-cooled oil coolers. U.S. Patent No. 4,708,199 shows several different connection variants and flow patterns through the oil cooler. A common feature of all variants is that the heat exchanger plates are arranged so that the passage openings in the heat exchanger plates form channels that pass through the stack of heat exchanger plates, through which a medium enters or leaves. On entry, the medium is distributed to the individual flow channels between the plates connected to the channels, in order to be collected at the output in the corresponding outlet channel before it leaves the heat exchanger. The flow channels between the plates alternate. A flow channel for oil, for example, is followed by a flow channel for water and so forth. The advantage of such a heat exchanger consists of its compact design, and that only two different types of heat exchanger plates are necessary.
However, for many applications, these heat exchangers have unduly low heat exchange performance, because the flow path through the heat exchanger is short. Moreover, the two types of heat exchanger plates have significant differences in shaping, which is a manufacturing drawback.
There is also a heat exchanger with a housing, in which a stack of two plates is arranged. In this heat exchanger one medium flows through the flow channels into the two plates, and the other medium flows into the housing and then through flow channels arranged between the two plates. It is known in such heat exchangers that the media can be made to flow in serpentine fashion through the heat exchanger by arranging baffles, or the like, in the flow channels. However, such heat exchangers are too costly to manufacture, are much more material-intensive and are therefore heavier than the heat exchangers of the aforementioned type at comparable performance.